Lamniformes
Class Chondrichthyes *Order Lamniformes *Family †Alopiidae *Family †Cretoxhyrhinidae *Family Lamnidae *Family Otodontidae *Family Odontaspididae These sharks are some of the most common sharks alive today. They first appeared during the early Cretaceous, though some teeth dating to the late Jurassic that possibly belong to Lamniformes have been found. As with most cartilaginous fish, preservation isn't that good, but on occasion beautiful specimens have been found. These early forms were the †Alopiidae. These aren't that well known, with only jaws and teeth that have been found. However, the jaws are remarkably similar to crocodile sharks in our world, and the teeth are rather larger compared to most modern Lamniformes, which suggests that they ate small fish. From the jaws it is presumed that they grew up to a metre long. The jaw structure and teeth show that they are the ancestors to all Lamniformes. Their fossil record lasted only into the Albian epoch. †Cretoxyrhinidae are a recently described group of Lamniformes that have been dated from the Santonian epoch to the Eocene epoch of North America. These are much more complete than †Alopiidae. These were slightly larger than †Alopiidae, at around 1.5 metres, but the teeth are different. The teeth are mostly cusps, the same used to crush hard shelled animals, meaning †Cretoxyrhinidae are bottom feeders, and feed on bivalves and arthropods, but it is suggested that they may have eaten fish from time to time. They are known to inhabit the Inland Sea and possibly lakes. These were an off shoot of the †Alopiidae, and leave no descendants, and have been classified as stem-lamniformes. The first modern Lamniformes to appear in the fossil record are the Lamnidae. These are slightly larger, up to 2 metres or more. Their teeth are mostly small, and most species are planktivorous. Probeaglea carolensis is the largest species, seen off the coast of South Africa. The four metre shark bares a striking resemblance to the great white shark, but it feeds on plankton and small fish. Most Lamnidae are deep sea, and resemble sixgilled sharks or tiger sharks. Those that are coastal species in South Africa are the main prey item for the macropredatory ichthyosaurs that live there. Today over 42 extant taxa have been found, and 12 extinct taxa have been found, starting from the Paleocene. These are the earliest crown-Lamniformes. Appearing shortly after the Lamnidae are the Odontaspididae. These are slightly larger, up to eight metres long, and inhabit both the deep sea and the coastal areas. In fact the largest species, Odontaspis mackrelei, lives in a coral reef off the coast of South Africa. This species is similar to a sand tiger shark, but they are harmless. Researchers that have dived with them all report that they are highly curious and playful. They are planktivores, that will occasionally eat squid and small fish. Despite their size they are vulnerable to ichthyosaur attacks, and are considered one of the most preyed upon species of sharks in the region. The rarest modern Lamniformes are the Otodontidae. These sharks share features of Odontaspidids and Lamnids, with recent DNA and morphological studies concluding them to be an intermediary form between Lamnids and Odontaspidids. They first appeared during the Oligocene, and soon shot off into bizarre forms. Some were metre long predators that hunted small fish, but some evolved into the biggest fishes of all time. The biggest species, Carcharoclesa gigantodon, lives along the equatorial belt of the Atlantic Ocean, and can grow up to 15 metres long and weigh a staggering 30 tonnes. They are the only Otodontids that are still extant. They are classified as vulnerable, and the band along the equator where the plankton and fishes are abundant gets smaller every year, meaning that they will soon go extinct. Otodontids are important to Lamniforme evolution. Lamnids were more piscivorous than planktivorous, the Otodontids were equally both, and the Odontaspidids are nearly entirely planktivorous. In the fossil record these sharks were scattered all over the world, but the Cape, off the coast of South Africa, has the richest diversity of Lamniformes anywhere in the world today. This might be because there are so many different types of prey for them to feed on, but this still remains a mystery. These are the most fantastical sharks alive today, and are found in every ocean on the planet. Another unique feature is that they are endothermic. Lamnids and Otodontids are gigantotherms, but Odontaspidids are entirely homeothermic.